1. Field of the Invention:
The present invention relates to apparatus and methods for displaying graphic information. More particularly, the present invention relates to direct memory access (DMA) apparatus and methods for generating and manipulating images and data on a display system.
2. Art Background:
In the computing industry, it is quite common to represent and convey information to a user through graphic representations. These representations may take a variety of forms, such as for example, alphanumeric characters, cartesian or other coordinate graphs, as well as shapes of well-known physical objects. Historically, humans have interfaced with computers through a system of discrete commands which typically comprise a combination of both text and mathematical symbolic characters. Examples of such systems are numerous and include the programming languages of FORTRAN, ALGOL, PLl, BASIC, and COBAL, which transform a given set of user commands into machine executable "object" code.
However, the ease with which a user becomes proficient in programming or interacting with the computer based system is generally a function of how close the system models the logical thought of the user himself. One system which has been developed to minimize the learning and acclimation period in which a user must go through to become proficient in the interaction with a computer system is frequently referred to as an "object oriented" system. This system may utilize multiple "windows" displayed on a cathode ray tube (CRT) in which combinations of text and graphics are used to convey information. For example, each window may take the form of a file folder, of the type used in a standard filing cabinet, overlapping other folders, with the "top" fully visible folder constituting the current work file. A user may add or delete information from a window, refile the file folder in another location, and generally operate with the windows just as if actual files in an office were being used. Thus, by graphically presenting an image which represents the object of the users command, and allow the user to operate on and manipulate the image in substantially the same way as he would as if the image constituted the actual object, the machine becomes easier to operate to the user and a stronger machine-man interface is achieved.
One historic limitation on the use of window based displays is in the case where animation within a window is desired. In such event, a series of sequential frames of data are displayed within a window over time, thereby appearing to the user as if the object displayed is animated, such as in a television or movie presentation. However, speed limitations in accessing memory have historically rendered animation of images difficult to achieve. The time which the central processing unit (CPU) requires to read data comprising an image from memory and then display such data was generally rather slow, and the images did not appear to "move" from one frame to another in a continuous and fluid fashion. As will be described, the present invention provides a direct memory access (DMA) system which permits images stored in memory to be displayed within a window on a CRT at a rate which permits an animation effect to be achieved.